Coriolis mass flow rate/density/viscoy sensor with two bent measuring tubes

ABSTRACT

This sensor ( 10 ) generates accurate measuring results, for example with an error in the order of  0.5 % of the measuring value, hat has mimimized production costs as well as a shorter overall length compared to that of conventional sensors. The sensor has two parallel V shaped measuring tubes ( 1, 2 ) each being of one-piece construction. Each tube has a straight inlet portion ( 11, 21 ), a straight outlet portion ( 12, 22 ), an inlet bend ( 13, 23 ) connected with the inlet portion, an outlet bend ( 14, 24 ) connected with the outlet portion, a straight tube portion ( 15, 25 ) connected with the inlet bend, a straight tube portion ( 16, 26 ) connected with the outlet bend, and a vertex bend ( 17, 27 ) connected with the first and second straight tube portions. The inlet portions ( 11, 21 ) are fixed in an inlet manifold ( 18 ) and the outlet portions in an outlet manifold ( 19 ); the manifolds ( 18, 19 ) are mounted in a support frame ( 30 ) which forms part of a housing ( 3 ). An excitation arrangement ( 6 ) causes the measuring tubes ( 1, 2 ) to vibrate as a tuning fork. Interspaced sensor elements ( 7, 8 ) are fixed to the measuring tubes. Mounted in the support frame ( 30 ) is a feedthrough ( 37 ) for a printed-circuit board ( 96 ) having conducting tracks ( 97 ) to which leads ( 63, 64, 73, 74, 83, 84 ) of the excitation system ( 6 ) and of the sensor elements ( 7, 8 ) are connected.

BACKGROUND AND SUMMARY OF THE INVENTION

[0001] This invention relates to a mass flow rate/density/viscositysensor working on the Coriolis principle—herein-after referred to as aCoriolis sensor for short—and comprising two bent measuring tubes.

[0002] With such Coriolis sensors, whose measuring tubes, as is wellknown, are set into vibration, particularly into flexural vibration withor without superposed torsional vibration, it is possible to measure notonly the instantaneous mass flow rate of a fluid flowing in a pipe, butalso the density of the fluid via the instantaneous vibration frequencyof the measuring tubes and the viscosity of the fluid via the powerrequired to maintain the vibrations of the tubes.

[0003] Since the temperature of the fluid is not constant duringoperation of the Coriolis sensor, and the density of the fluid, as iswell known, is temperature-dependent, the Coriolis sensor is commonlyprovided with at least one temperature sensor for measuring thetemperature of the fluid. For all those measurements, the Coriolissensor is connected into the pipe in a pressure-tight manner andgenerally permanently, for example via flanges.

[0004] U.S. Pat. No. 4,187,721 discloses a Coriolis mass flowrate/density sensor designed to be installed in a pipe through which afluid flows at least temporarily, and comprising:

[0005] a single, U-shaped measuring tube bent in one plane symmetricallywith respect to an axis of symmetry, which

[0006] is of one-piece construction and

[0007] has a straight inlet portion fixed in a support angle,

[0008] a straight outlet portion fixed in the support angle,

[0009] an offset inlet transition portion connected with the inletportion,

[0010] an offset outlet transition portion connected with the outletportion,

[0011] a first bent portion connected with the inlet transition portion,

[0012] a second bent portion connected with the outlet transitionportion,

[0013] a straight base portion connecting the first and second bentportions;

[0014] an excitation system

[0015] which in operation causes the measuring tube together with anexciter carrier to vibrate as a tuning fork,

[0016] a first portion of which is fixed to the base portion in the areaof the axis of symmetry, and

[0017] a second portion of which is fixed to the exciter carrier;

[0018] a first optical sensor,

[0019] a first portion of which is fixed to the measuring tube at alocation

[0020] where the inlet transition portion passes into the first bentportion, and

[0021] a second portion of which is fixed to the support angle; and

[0022] a second optical sensor,

[0023] a first portion of which is fixed to the measuring tube at alocation

[0024] where the outlet transition portion passes into the second bentportion, and

[0025] a second portion of which is fixed to the support angle.

[0026] JP-A 56-125 622 discloses a Coriolis mass flow rate sensordesigned to be installed in a pipe through which a fluid flows at leasttemporarily, and comprising:

[0027] an omega-shaped measuring tube bent in one plane symmetricallywith respect to an axis of symmetry which

[0028] is of one-piece construction and

[0029] has a straight inlet portion with an inlet axis lying in saidplane,

[0030] a straight outlet portion with an outlet axis aligned with theinlet axis,

[0031] an S-shaped inlet bend connected with the inlet portion,

[0032] an S-shaped outlet bend connected with the outlet portion, and

[0033] a vertex bend connecting the inlet and outlet bends;

[0034] an excitation system

[0035] which in operation causes the measuring tube together with anexciter carrier to vibrate as a tuning fork,

[0036] a first portion of which is fixed to the vertex bend in the areaof the axis of synunetry, and

[0037] a second portion of which is fixed to the exciter carrier;

[0038] a bar-shaped sensor carrier

[0039] which extends perpendicular to the axis of symmetry,

[0040] a first end of which is fixed to the measuring tube at a locationwhere the inlet bend passes into the vertex bend, and

[0041] a second end of which is fixed to the measuring tube at alocation where the outlet bend passes into the vertex bend; and

[0042] a strain-gage bridge disposed as a sensor arrangement on thesensor carrier.

[0043] U.S. Pat. No. 4,127,028 discloses a Coriolis mass flow ratesensor designed to be installed in a pipe through which a fluid flows atleast temporarily, and comprising:

[0044] a first U-shaped measuring tube bent in a first planesymmetrically with respect to a first axis of symmetry;

[0045] a second U-shaped measuring tube bent in a second planesymmetrically with respect to a second axis of syimnetry,

[0046] which measuring tubes are arranged parallel to each other, are ofone-piece construction, and are connected in series in terms of fluidflow, and

[0047] each of which measuring tubes has

[0048] a straight inlet portion,

[0049] a straight outlet portion,

[0050] an S-shaped inlet bend connected with the inlet portion,

[0051] an S-shaped outlet bend connected with the outlet portion,

[0052] a first straight tube portion connected with the inlet bend,

[0053] a second straight tube portion connected with the outlet bend,and

[0054] a semicircular base bend connected with the first and secondstraight tube portions,

[0055] which inlet and outlet portions extend through a fixed member,

[0056] with the distance between the inlet and outlet portions of eachmeasuring tube being less than the distance between the first and secondstraight tube portions of the respective measuring tube;

[0057] an excitation system

[0058] which during operation causes the measuring tubes to vibrate as atuning fork,

[0059] a first portion of which is fixed to the semicircular base bendof the first measuring tube in the area of the axis of symmetry of thefirst measuring tube, and

[0060] a second portion of which is fixed to the semicircular base bendof the second measuring tube in the area of the axis of symmetry of thesecond measuring tube;

[0061] a first optical sensor,

[0062] a first portion of which is fixed to the first measuring tube anda second portion of which is fixed to the second measuring tube atrespective locations

[0063] where the respective first straight tube portion passes into therespective semicircular base bend; and

[0064] a second optical sensor,

[0065] a first portion of which is fixed to the first measuring tube anda second portion of which is fixed to the second measuring tube atrespective locations

[0066] where the respective second straight tube portion passes into therespective semicircular base bend.

[0067] U.S. Pat. No. 4,622,858 discloses a Coriolis mass flow ratesensor designed to be installed in a pipe through which a fluid flows atleast temporarily, and comprising:

[0068] a first straight measuring tube;

[0069] a second straight measuring tube,

[0070] which measuring tubes are arranged parallel to each other,

[0071] are of one-piece construction, and

[0072] are connected in parallel in terms of fluid flow by means of aninlet manifold and an outlet manifold;

[0073] a driving mechanism

[0074] which in operation vibrates the measuring tubes as a tuning fork,

[0075] a first portion of which is fixed to the first measuring tubemidway between the inlet manifold and the outlet manifold, and

[0076] a second portion of which is fixed to the second measuring tubemidway between the inlet manifold and the outlet manifold;

[0077] a first electrodynamic sensor,

[0078] a first portion of which is fixed to the first measuring tubemidway between the driving mechanism and the inlet manifold, and asecond portion of which is fixed to the second measuring tube midwaybetween the driving mechanism and the inlet manifold; and

[0079] a second electrodynamic sensor,

[0080] a first portion of which is fixed to the first measuring tubemidway between the driving mechanism and the outlet manifold, and asecond portion of which is fixed to the second measuring tube midwaybetween the driving mechanism and the outlet manifold.

[0081] U.S. Pat. No. 6,006,609 discloses a Coriolis mass flowrate/density/viscosity sensor designed to be installed in a pipe throughwhich a fluid flows at least temporarily, and comprising:

[0082] a single straight measuring tube of one-piece construction

[0083] which is provided with a cantilever at its midpoint, and

[0084] an inlet end and an outlet end of which are mounted in a supportframe which is disposed in a housing;

[0085] an excitation arrangement

[0086] which in operation sets the measuring tube into flexuralvibrations and into torsional vibrations equal in frequency to theflexural vibrations, and

[0087] first portions of which are fixed to the cantilever and secondportions of which are fixed to the support frame;

[0088] a first sensor,

[0089] a first and a second portion of which are fixed to the measuringtube and the support frame, respectively, approximately midway betweenthe inlet end and the cantilever; and

[0090] a second sensor,

[0091] a first and a second portion of which are fixed to the measuringtube and the support frame, respectively, approximately midway betweenthe outlet end and the cantilever.

[0092] U.S. Pat. No. 5,796,011, particularly in connection with FIG. 5,describes a Coriolis mass flow rate sensor designed to be installed in apipe through which a fluid flows at least temporarily, and comprising:

[0093] a first measuring tube bent in a first plane symmetrically withrespect to a first axis of symmetry;

[0094] a second measuring tube bent in a second plane symmetrically withrespect to a second axis of symmetry,

[0095] which measuring tubes are arranged parallel to each other and areof one-piece construction, and

[0096] each of which measuring tubes has

[0097] a straight inlet portion with an inlet axis lying in the firstplane and the second plane, respectively,

[0098] a straight outlet portion with an outlet axis aligned with theinlet axis,

[0099] an inlet bend connected with the inlet portion,

[0100] an outlet bend connected with the outlet portion, and

[0101] a circular-arc-shaped vertex portion of minimum height connectedwith the inlet bend and outlet bend,

[0102] which inlet portions and which outlet portions are connected inparallel in terms of fluid flow by means of an inlet manifold and anoutlet manifold, respectively, and

[0103] which manifolds are mounted in a support frame which forms partof a housing;

[0104] a first node plate rigidly connecting the two measuring tubes ata location

[0105] where the inlet bend passes into die circular-arc-shaped vertexbend;

[0106] a second node plate rigidly connecting the two measuring tubes ata location

[0107] where the outlet bend passes into the circular-arc-shaped vertexbend;

[0108] an excitation system

[0109] which in operation causes the measuring tubes to vibrate as atuning fork,

[0110] a first portion of which Is fixed to the circular-arc-shapedvertex bend of the first measuring tube in the area of the axis ofsymmetry of the first measuring tube, and

[0111] a second portion of which is fixed to the circular-arc-shapedvertex bend of the second measuring tube in the area of the axis ofsynmtetry of the second measuring tube;

[0112] a first sensor,

[0113] a first portion of which is fixed to the first measuring tube anda second portion of which is fixed to the second measuring tube atrespective locations

[0114] where the respective inlet bend passes into the respectivecircular-arc-shaped vertex bend;

[0115] a second sensor,

[0116] a first portion of which fixed to the first measuring tube and asecond portion of which is fixed to the second measuring tube atrespective locations

[0117] where the respective outlet bend passes into the respectivecircular-arc-shaped vertex bend;

[0118] a feedthrough mounted in the support frame opposite thecircular-arc-shaped vertex bends and containing several electricconductors; and

[0119] a printed-circuit board attached to the support frame andextending between the inlet manifold and outlet manifold and havingconducting tracks

[0120] via which leads of the excitation system and the sensors areconnected to the conductors of the feedthrough.

[0121] To the above referred ensembles of features of the individualprior-art arrangements it should be added that a straight measuring tubeor straight measuring tubes are preferably made of pure titanium, ahigh-titaniuin alloy, pure zirconium, or a high-zirconium alloy, since,compared with measuring tubes of stainless steel, which is suitablematerial for straight measuring tubes in principle, shorter overalllengths are obtained, and that a bent measuring tube or bent measuringtubes are preferably made of stainless steel, although titanium orzirconium or their alloys are suitable materials for such tubes as well.

[0122] The design principle of the Coriolis mass flow rate sensoraccording to U.S. Pat. No. 5,796,011 permits the use of only suchcircular-arc vertex bends which have a great radius of curvature, i.e.,where the distance between the circular-arc vertex bend and theinlet/outlet axis is minimal as a function of the inside diameter andthe wall thickness of the measuring tubes and of a permissible,temperature-range-induced mechanical stress. For distances between thevertex and the inlet/outlet axis that are greater than the minimumdistance, however, particularly for distances greater than the minimumdistance by an order of magnitude, the design principle of US. Pat. No.5,796,011 is unsuitable.

[0123] Therefore, starting from the design principle U.S. Pat. No.5,796,011, it is an object of the invention to provide a Coriolis massflow rate/density/viscosity sensor in which the distance between thevertex of the vertex bend and the inlet/outlet axis can be virtuallyarbitrarily great. At the same time, high measurement accuracy, forexample of the order of ±0.5%, is to be achievable, manufacturing costsare to be minimized as compared to those of prior-art mass flow ratesensors, mass flow rate/density sensors, or mass flowrate/density/viscosity sensors, and a shorter overall length is to bemade possible.

[0124] To attain these objects, the invention provides a Coriolis massflow rate/density/viscosity sensor designed to be installed in a pipethrough which a fluid flows at least temporarily, and comprising:

[0125] a first measuring tube bent to a V shape in a first planesymmetrically with respect to a first axis of symmetry;

[0126] a second measuring tube bent to a V shape in a second planesymmetrically with respect to a second axis of symmetry,

[0127] which measuring tubes are arranged parallel to each other and areeach of one-piece construction, and

[0128] each of which measuring tubes has

[0129] a straight inlet portion with an inlet axis lying in the firstplane and second plane, respectively,

[0130] a straight outlet portion with an outlet axis lying in the firstplane and second plane, respectively, and aligned with the inlet axis,

[0131] an inlet bend connected with the inlet portion,

[0132] an outlet bend connected with the outlet portion,

[0133] a first straight tube portion connected with the inlet bend,

[0134] a second straight tube portion connected with the outlet bend,and

[0135] a vertex bend connected with the first and second straight tubeportions,

[0136] which inlet portions are fixed in an inlet manifold, which outletportions are fixed in an outlet manifold, and

[0137] which manifolds are mounted in a support frame which forms partof a housing;

[0138] an excitation arrangement

[0139] which in operation causes the measuring tubes to vibrate as atuning fork,

[0140] a first portion of which is fixed to the vertex bend of the firstmeasuring tube in the area of the axis of symmetry of the firstmeasuring tube, and

[0141] a second portion of which is fixed to the vertex bend of thesecond measuring tube in the area of the axis of symmetry of the secondmeasuring tube;

[0142] a first velocity or displacement sensor,

[0143] a first portion of which is fixed to the first straight tubeportion of the first measuring tube, and

[0144] a second portion of which is fixed to the first straight tubeportion of the second measuring tube;

[0145] a second velocity or displacement sensor, positionedsymmetrically with respect to the axes of symmetry of the measuringtubes,

[0146] a first portion of which is fixed to the second straight tubeportion of the first measuring tube, and a second portion of which isfixed to the second straight tube portion of the second measuring tube;

[0147] a feedthrough mounted in the support frame opposite the vertexbends and containing several electric conductors; and

[0148] a printed-circuit board attached to the support frame andextending between the support frame and the vertex bends and havingconducting tracks

[0149] to which leads of the excitation system and of the velocity ordisplacement sensors are connected.

[0150] In a preferred embodiment of the invention, the measuring tubes

[0151] are rigidly connected by a first node plate in the vicinity of alocation

[0152] where the respective inlet portion passes into the respectiveinlet bend,

[0153] are rigidly connected by a second node plate in the vicinity of alocation

[0154] where the respective inlet bend passes into the respective firststraight tube portion,

[0155] are rigidly connected by a third node plate in the vicinity of alocation

[0156] where the respective outlet portion passes into the respectiveoutlet bend, and

[0157] are rigidly connected by a fourth node plate in the vicintiy of alocation

[0158] where the respective outlet bend passes into the respectivesecond straight tube portion.

[0159] According to a first development of the invention and/or of theabove preferred embodiment, electrodynamic velocity sensors are used andthe excitation system is of the electrodynamic type.

[0160] According to a second development of the invention, which canalso be used with the above preferred embodiment and/or the firstdevelopment,

[0161] the support frame is of one-piece construction and is made ofstainless sheet steel of constant width and thickness having a frontface and a rear face, comprises:

[0162] a plane inlet frame portion, which has the inlet manifold weldedtherein,

[0163] a plane outlet frame portion, which has the outlet manifoldwelded therein,

[0164] a plane feedthrough frame portion connecting the inlet frameportion and outlet frame portion and having the feedthrough mountedtherein in a pressure-tight manner,

[0165] a first plane extension frame portion extending from the inletframe portion at an angle greater than 90°,

[0166] a bent vertex frame portion passing into the first extensionframe portion, and

[0167] a second plane extension frame portion extending from the outletframe portion at said angle and passing into the vertex frame portion;and

[0168] the support frame is supplemented by a plane front sheet ofstainless steel, which is welded to the front, and a plane rear sheet ofthe same steel, which is welded to the rear face, to form the housing.

[0169] According to a third development of the invention, which can alsobe used with the preferred embodiment and/or the first and/or seconddevelopments, the feedthrough comprises:

[0170] a flange attached to the support frame and having a hole;

[0171] the printed-circuit board, which is passed through a slot formedin the feedthrough frame portion and extends into the flange, with theprinted-circuit board and the slot separated by a distance sufficientfor electric isolation;

[0172] a disk of insulating material resting on the feedthrough frameportion and through which the printed-circuit board is passed; and

[0173] an insulating compound filling a portion of the hole lying abovethe disk, the insulating compound having a thickness at least equal tothe gap length specified for type of protection Ex-d as a function ofgap width.

[0174] One advantage of the invention is that it permits theconstruction of Coriolis mass flow rate/density/viscosity sensors whoseoverall length, i.e., the length along the inlet/outlet axis, isconsiderably shorter than the overall length of the assembly accordingto U.S. Pat. No. 5,796,011. This is due to, among other things, the Vshape of the measuring tube. A compact sensor with the desiredmeasurement accuracy is obtained.

[0175] Furthermore, the design of the housing, which consistsessentially of a support frame, a front steel sheet, and a rear steelsheet, contributes to the fact that the Coriolis sensor can bemanufactured at very bw cost. Manufacturing costs are also kept lowthrough the use of the printed-circuit board for the feedthrough, sincethe board provides a simple and low-cost electrical connection betweenthe excitation system and the sensors on the one hand and evaluationelectronics on the other.

BRIEF DESCRIPTION OF THE DRAWINGS

[0176] The invention will now be explained in more detail with referenceto the accompanying drawings, which show a preferred embodiment of theinvention. Corresponding components are designated by the same referencenumerals throughout the various figures, but reference numerals arerepeated in subsequent figures only if this appears appropriate. In thedrawings:

[0177]FIG. 1 is a perspective view showing mechanical details of aCoriolis sensor, with its housing not completed;

[0178]FIG. 2 is a front view of the Coriolis sensor of FIG. 1, againwith its housing not completed, but with additional electrical details;

[0179]FIG. 3 is a section taken along line A-A of FIG. 2, showing theCoriolis sensor in a plan view, but with the housing completed; and

[0180]FIG. 4 is a section taken along line B-B of FIG. 2, showing theCoriolis sensor in a side view and again with the housing completed.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0181] While the invention is susceptible to various modifications andalternative forms, exemplary embodiments thereof have been shown by wayof example in the drawings and will herein be described in detail. Itshould be understood, however, that there is no intent to limit theinvention to the particular forms desclosed, but on the contrary, theinvention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theappended claims.

[0182]FIG. 1 is a perspective view showing only mechanical details of aCoriolis mass flow rate/density/viscosity sensor, referred to herein asa Coriolis sensor 10 for short, but with its housing not completed inorder to more clearly show its internal construction, and FIG. 2 is acorresponding front view with additional electrical details.

[0183]FIGS. 3 and 4 are sectional views of FIG. 2 with the housingcompleted. Because of the representation chosen, a perspective FIG. 1along with front, plan, and side views, in the following the figures aredescribed not one after the other, but together.

[0184] Coriolis sensor 10 has a first V-shaped measuring tube 1, whichis bent in a first plane symmetrically with respect to a first axis ofsymmetry. A second V-shaped measuring tube 2 is bent in a second planesymmetrically with with respect to a second axis of symmetry. Measuringtubes 1, 2 are arranged parallel to each other, and each of them is ofone-piece construction.

[0185] Measuring tube 1 has a straight inlet portion 11 with an inletaxis lying in the first plane, and a straight outlet portion 12 with anoutlet axis lying in the first plane and aligned with the inlet axis; acommon axis is thus obtained, which will hereinafter be referred to asan inlet/outlet axis.

[0186] Measuring tube 2 has a straight inlet portion 21 with an inletaxis lying in the second plane, a straight outlet portion 22 (visibleonly in FIG. 3) with an outlet axis lying in the second plane andaligned with the inlet axis; this common axis, too, will hereinafter bereferred to as an inlet/outlet axis.

[0187] Measuring tube 1 further has an inlet bend 13 connected withinlet portion 11, an outlet bend 14 connected with outlet portion 12, afirst straight tube portion 15 connected with inlet bend 13, a secondstraight tube portion 16 connected with outlet bend 14, and a vertexbend 17 connected with the first and second straight tube portions 15,16.

[0188] Measuring tube 2 further has an inlet bend 23 connected withinlet portion 21, and outlet bend 24 (visible only in FIG. 3) connectedwith outlet portion 22, a first straight tube portion 25 connected withinlet bend 23, a second straight tube portion 26 connected with outletbend 24, and a vertex bend 27 connected with the straight tube portions25, 26. In the embodiment shown, the curvature of the axis of vertexbend 17 and that of vertex bend 27 coreespond practically to the arc ofa circle.

[0189] Inlet portions 11, 21 are fixed in an inlet manifold 18,andoutlet portions 12, 22 are fixed in an outlet manifold 19. Thesemanifolds 18, 19 are mounted in a support frame 30, which forms part ofa housing 3 (visible only in FIGS. 3 and 4).

[0190] In the embodiment, measuring tubes 1, 2 and manifolds 18, 19 aremade of stainless steel. Preferably, the stainless steel with theEuropean material number 1.4539, corresponding to the Americandesignation 904 L, is used for measuring tubes 1, 2, and the stainlesssteel with the European material number 1.4404, corresponding to theAmerican designation 316 L, is used for manifolds 18, 19.

[0191] Coriolis sensor 10 is designed to be installed in a pipe throughwhich a fluid to be measured flows at least temporarily. To that end,the manufacturer provides inlet and outlet manifolds 18, 19 withcustomized connection means, such as connections with an internal orexternal thread, flanges, or clamping devices as are commerciallyavailable, for example, under the registered trademark Triclamp.

[0192] Like measuring tubes 1, 2, support frame 30 is of one-piececonstruction. It was made from a flat bar of high-grade steel and ofconstant width and thickness by suitably bending the bar and welding itsends, see the joint 33, and it has a front face 31 and a rear face 32(visible only in FIGS. 3 and 4).

[0193] Support frame 30 comprises a plane inlet frame portion 34, inwhich inlet manifold 18 is fixed by welding, and a plane outlet frameportion 35, in which outlet manifold 19 is fixed by welding, see in FIG.2 the portions 18 and 19 protruding from support frame 30, withassociated welds 18′ and 19′, respectively.

[0194] Support frame 30 further comprises a plane feedthrough frameportion 36, which connects inlet frame portion 34 and outlet frameportion 35, and in which a feedthrough 37 (visible only in FIG. 4) isfixed in a pressure-tight manner. Feedthrough frame portion 36 formsrespective right angles with inlet and outlet frame portions 34, 35.

[0195] Support frame 30 further comprises a first plane extensionportion 38, which extends from inlet frame portion 34 at an anglegreater than 90°, in the embodiment approximately 120°. Support frame 30finally comprises a bent vertex portion 39, which passes into extensionportion 38, and a second plane extension portion 40, which extends fromoutlet frame portion 35 at the above-mentioned angle and passes intovertex portion 39.

[0196] Support frame 30 is supplemented by a plane front sheet 41 ofstainless steel welded to front face 31 and a preferably plane rearsheet 42 of the same steel welded to rear face 32 to form the housing 3,50 that the latter is pressure-tight. Front and rear sheets 41, 42 canonly be seen in FIGS. 3 and 4. In the embodiment, the steel preferablyused for housing 3 is the stainless steel with the European materialnumber 1.4301, which corresponds to the American designation 304.

[0197] The preferably plane front and rear sheets 41, 42 result in ahigher stiffness of housing 3 under compressive stress in the directionof the inlet/outlet axis than if these sheets were provided withlongitudinal crimps. Measuring tubes 1, 2 are rigidly connected by afirst node plate 51 in the vicinity of a location where the respectiveinlet portion 11, 21 passes into the respective inlet bend 13, 23, andby a second mode plate 52 in the vicinity of a location where therespective inlet bend 13, 23 passes into the respective first straighttube portion 15, 25.

[0198] Furthermore, measuring tubes 1, 2 are rigidly connected by athird node plate 53 in the vicinity of a location where the respectiveoutlet portion 12, 22 passes into the respective outlet bend 14, 24, andby a fourth node plate 54 in the vicinity of a location where therespective outlet bend 14, 24 passes into the respective second straighttube portion 16, 26.

[0199] The four node plates 51, 52, 53, 54 are preferably thin plates ofstainless steel, particularly of the same steel as that used for housing3. These plates are provided with holes whose diameters correspond tothe outside diameters of measuring tubes 1, 2, and with slots, so thatthey can be first clamped onto and then brazed to measuring tubes 1, 2,with the slots being brazed together as well, so that the plates areseated on measuring tubes 1, 2 unslotted as node plates.

[0200] In operation, an excitation system 6 vibrates measuring tubes 1,2 as a tuning fork at a frequency equal or close to the mechanicalresonance frequency of the vibrating system formed by measuring tubes 1,2. This vibration frequency, as is well known, is dependent on thedensity of the fluid flowing through measuring tubes 1, 2. Therefore,the density of the fluid can be determined from the vibration frequency.

[0201] A first portion 61 of excitation system 6 is fixed to vertex bend17 of measuring tube 1 in the area of the above-mentioned axis ofsymmetry of this tube, and a second portion 62 of excitation system 6 isfixed to vertex bend 27 of measuring tube 2 in the area of theabove-mentioned axis of symmetry of this tube, see FIG.4.

[0202] In the embodiment shown in the figures, excitation system 6 is anelectrodynamic shaker, i.e., portion 61 is a coil and portion 62 apermanent magnet that cooperates with the coil by riding therein.

[0203] Excitation system 6 is supplied with AC power from a drivercircuit (not shown), which may, for instance, be a PLL circuit thatcontinuously adjusts the instantaneous resonance frequency of thevibrating system of measuring tubes 1, 2. Such a PLL circuit isdisclosed in U.S. Pat. No. 4,801,897, the disclosure of which is herebyincorporated by reference.

[0204] A first velocity or displacement sensor 7 and a second velocityor displacement sensor 8, which are mounted on measuring tubes 1, 2symmetrically with respect to the aforementioned axes of symmetry,produce measurement signals from which the mass flow rate, the density,and, if desired, the viscosity of the fluid can be determined.

[0205] A first portion 71 of velocity or displacement sensor 7 is fixedto the straight portion 15 of measuring tube 1, and a second portion iZis fixed to the straight portion 25 of measuring tube 2, see FIG. 3. Afirst portion 81 of velocity or displacement sensor 8 is fixed to thestraight portion 16 of measuring tube 1, and a second portion 82 isfixed to the straight portion 26 of measuring tube 2, see FIG. 3.

[0206] In the embodiment shown in the figures, velocity or displacementsensors 7, 8 are preferably electrodynamic velocity sensors; thus, eachof portions 71, 81 is a coil, and each of portion 72, 82 is a permanentmagnet that can ride in the associated coil.

[0207] As already briefly mentioned above, feedthrough 37, whichcontains several electric conductors, is mounted in support frame 30opposite vertex bends 17, 27, and thus opposite vertex frame portion 39,particularly in a pressure-tight manner. To that end, a flange 90 isattached to support frame 30; preferably, flange 90 is welded to supportframe 30. Flange 90 has a hole 91, so that feedthrough 37 is accessiblefrom outside housing 3.

[0208] Feedthrough 37 comprises a printed-circuit board 96, which isfastened to support frame 30 by means of an angled support plate 95 andwhich extends between support frame 30 and the vertex bends toward thelatter. Printedcircuit board 96 has conducting tracks formed thereon,cf. conducting track 97, which are only visible in FIG.2.

[0209] Connected to respective ones of these conducting tracks are leads63, 64 of excitation system 6, leads 73, 74 of velocity sensor 7, leads83, 84 of velocity sensor 8, and leads 93, 94 of a temperature sensor 9,which are thus also connectect to the individual conductors otfeedthrough 37. Leads 63, 64, 73, 74, 83, 84, 93, 94 can only be seen inFIG. 2. In addition, a conducting track SN to ground is provided on theprinted-circuit board, which is mechanically and, thus, electricallyattached to the metallic support plate 95.

[0210] In the embodiment shown, temperature sensor 9 (visible only inFIGS. 2 and 3) is attached to outlet bend 14 of measuring tube 1, forinstance with adhesive, and is preferably a platinum resistance element.As mentioned above, it serves to measure the current temperature of thefluid. Temperature sensor 9 may also be positioned at any other suitablelocation of measuring tubes 1, 2.

[0211] Feedthrough 37 further comprises a slot 361 formed in feedthroughframe portion 36, through which the printed-circuit board 96 is passedand extends into flange 90, with a distance sufficient for electricalisolation being maintained between printed circuit board 96 and slot361.

[0212] Furthermore, printed-circuit board 96 is passed through a disk362 of insulating material resting on feedthrough frame portion 36. Aninsulating compound 363 completely fills a portion of hole 91 lyingabove disk 362, and may also have penetrated into the space betweenprinted-circuit board 96 and the internal wall of slot 363.

[0213] The thickness of insulating compound 363 in the direction of theopen end of hole 91 is at least equal to the gap length required fortype of protection Ex-d according to European Standard EN 50014 and EN50018 as a function of gap width, the disclosures of which are herebyincorporated by reference. These standards correspond to comparablestandards of other countries.

[0214] As Coriolis sensor 10 has to be equipped with associated controland evaluation electronics to obtain an operational Coriolis mass flowrate/density/viscosity meter, a housing (not shown) for those controland evaluation electronics or a terminal arrangement (not shown) for acable running to a control and evaluation electronics housing remotefrom the Coriolis sensor is screwed to flange 90.

[0215] While the invention has been illustrated and described in detailin the drawing and foregoing description, such illustration anddescription is to be considered as exemplary and not restrictive incharacter, it beeing understood that only exemplary embodiments havebeen shown and described and that all changes and modifications thatcome within the spirit of the invention are desired to be protected.

What is claimed is:
 1. A Coriolis mass flow rate/density/viscositysensor designed to be installed in a pipe through which a fluid flows atleast temporarily, and comprising: a first measuring tube bent to a Vshape in a first plane symmetrically with respect to a first axis ofsymmetry; a second measuring tube bent to a V shape in a second planesymmetrically with respect to a second axis of symmetry, which measuringtubes are arranged parallel to each other and are each of one-piececonstruction, and each of which measuring tubes has a straight inletportion with an inlet axis lying in the first plane and second plane,respectively, a straight outlet portion with an outlet axis lying in thefirst plane and second plane, respectively, and aligned with the inletaxis, an inlet bend connected with the inlet portion, an outlet bendconnected with the outlet portion, a first straight tube portionconnected with the inlet bend, a second straight tube portion connectedwith the outlet bend, and a vertex bend connected with the first andsecond straight tube portions, which inlet portions are fixed in aninlet manifold, which outlet portions are fixed in an outlet manifold,and which manifolds are mounted in a support frame which forms part of ahousing; an excitation arrangement which in operation causes themeasuring tubes to vibrate as a tuning fork, a first portion of which isfixed to the vertex bend of the first measuring tube in the area of theaxis of symmetry of the first measuring tube, and a second portion ofwhich is fixed to the vertex bend of the second measuring tube in thearea of the axis of symmetry of the second measuring tube; a firstvelocity or displacement sensor, a first portion of which is fixed tothe first straight tube portion of the first measuring tube, and asecond portion of which is fixed to the first straight tube portion ofthe second measuring tube; a second velocity or displacement sensor,positioned symmetrically with respect to the axes of symmetry of themeasuring tubes, a first portion of which is fixed to the secondstraight tube portion of the first measuring tube, and a second portionof which is fixed to the second straight tube portion of the secondmeasuring tube; a feedthrough mounted in the support frame opposite thevertex bends and containing several electric conductors; and aprinted-circuit board attached to the support frame and extendingbetween the support frame and the vertex bends and having conductingtracks to which leads of the excitation system and of the velocity ordisplacement sensors are connected.
 2. The Coriolis mass flowrate/density/viscosity sensor as claimed in claim 1 wherein themeasuring tubes are rigidly connected by a first node plate in thevicinity of a location where the respective inlet portion passes intothe respective inlet bend, are rigidly connected by a second node platein the vicinity of a location where the respective inlet bend passesinto the respective first straight tube portion, are rigidly connectedby a third node plate in the vicinity of a location where the respectiveoutlet portion passes into the respective outlet bend, and are rigidlyconnected by a fourth node plate in the vicintiy of a location where therespective outlet bend passes into the respective second straight tubeportion.
 3. The Coriolis mass flow rate/density/viscosity sensor asclaimed in claim 1 or 2 wherein electrodynamic velocity sensors are usedand the excitation system is of the electrodynamic type.
 4. The Coriolismass flow rate/density/viscosity sensor as claimed in anyone of claims 1to 3 wherein the support frame is of one-piece construction and is madeof stainless sheet steel of constant width and thickness having a frontface and a rear face, comprises: a plane inlet frame portion, which hasthe inlet manifold welded therein, a plane outlet frame portion, whichhas the outlet manifold welded therein, a plane feedthrough frameportion connecting the inlet frame portion and outlet frame portion andhaving the feedthrough mounted therein in a pressure-tight manner, afirst plane extension frame portion extending from the inlet frameportion at an angle greater than 90°, a bent vertex frame portionpassing into the first extension frame portion, and a second planeextension frame portion extending from the outlet frame portion at saidangle and passing into the vertex frame portion; and the support frameis supplemented by a plane front sheet of stainless steel, which iswelded to the front, and a plane rear sheet of the same steel, which iswelded to the rear face, to form the housing.
 5. The Coriolis mass flowrate/density/viscosity sensor as claimed in anyone of claims 1 to 4wherein the feedthrough comprises: a flange attached to the supportframe and having a hole; the printed-circuit board, which is passedthrough a slot formed in the feedthrough frame portion and extends intothe flange, with the printed-circuit board and the slot separated by adistance sufficient for electric isolation; a disk of insulatingmaterial resting on the feedthrough frame portion and through which theprinted-circuit board is passed; and an insulating compound filling aportion of the hole lying above the disk, the insulating compound havinga thickness at least equal to the gap length specified for type ofprotection Ex-d as a function of gap width.